1) Field of the Invention
The present invention relates to a radio frequency identification (RFID) tag such as a non-contact integrated circuit (IC) card, which receives power supply and information from, and transmits information to, an external device. The “RFID tag” used in the present invention is also known to one skilled in the art as an “RFID tag inlay”, inlay being an internal constituent part (inlay) used in the “RFID tag”. The “RFID tag” is also known as a “wireless IC tag”.
2) Description of the Related Art
RFID tags such as a non-contact integrated circuit that receive using radio waves, power supply and information from an external device such as an IC card reader/writer and then transmit the received information to the external device contact-free are being used in recent years. A typical RFID tag includes an antenna pattern and an integrated circuit (IC) chip. The antenna pattern, which transmits and receives data, is mounted on a substrate made of plastic, paper, and the like. The antenna pattern and a capacity element built into the IC chip form a resonance circuit, and the RFID tag communicates via radio waves with the external device by means of the antenna pattern.
However, there may be instances where an RFID tag is used close to a wave-absorbing material such as a wine bottle or a human body. The wave-absorbing material poses a problem in the communication process since it absorbs the radio waves (for instance, radio waves in the ultra high frequency (UHF) band) that are required by the RFID tag for transmission and reception. FIG. 26 and FIG. 27 are drawings of conventional well-known means that enhance the gain of an antenna. FIG. 26 is a cross-sectional view of a conventional RFID tag in which a plane antenna is provided on the wave-absorbing material. FIG. 27 is a cross-sectional view of a conventional RFID tag in which a loop antenna is provided on the wave-absorbing material.
As shown in FIG. 26, a substrate 110 having a plane antenna 120 is fixed to a wave-absorbing material 100 by means of an adhesive 140. The plane antenna 120 is connected by means of a feeding point 130 to an IC chip (not shown) mounted on another substrate.
As a related conventional technology, the RFID tag with a plane coil antenna is well known (for instance, see Japanese Patent Laid-Open Publication No. 2004-206479). An RFID tag with a plane coil antenna includes a dielectric antenna substrate and an antenna coil. The antenna coil includes a first set of coils located on one surface of the antenna substrate and a second set of coils located on a second surface of the antenna substrate. The first set of coils and the second set of coils straddle the antenna substrate, each coil of the first set and each coil of the second set alternating with each other such that a portion of the two coils face each other. The first set of coils and the second set of coils are connected in a predetermined sequence.
As shown in FIG. 27, a loop antenna 160, which is in a sheet of a metal, is fixed on the wave-absorbing material 100 by means of the adhesive 140. The loop antenna 160 encloses a hollow interior 150 and is connected by means of the feeding point 130 to an IC chip (not shown) mounted on another substrate. The RFID loop antenna is widely used in pagers.
However, in a RFID tag with the plane antenna 110 shown in FIG. 26, an antenna pattern that has a small area can be employed. If the area of the antenna pattern is small, the communication distance is short. The wave-absorbing material 100 causes further degradation of antenna response because it absorbs the radio waves.
Similarly, the antenna response is affected and the communication distance also decreases significantly in the case of the RFID tag fabricated using a plane coil antenna disclosed in Japanese Patent Laid-Open Publication No. 2004-206479, since the wave-absorbing material 100 absorbs the radio waves.
However, in an RFID tag with a loop antenna 160 shown in FIG. 27, since the loop antenna 160 has a diameter, the antenna cannot be made slim. Therefore, the loop antenna can not be employed in small RFID tags.
Moreover, the loop antenna 160 may get crushed when subjected to external pressure since it has a hollow interior 150.